Convenient near-field optical measurement and analysis of polystyrene spheres

The modification of a commercial tapping mode atomic force microscope (AFM) into a transmission mode near-field scanning optical microscope (NSOM) is presented and polystyrene spheres in the diameter of 100 nm are used in this experiment. The detection of near-field signals is based on photodiodes with lock-in technique, and resolutions of topography and near-field signals obtained are about 10 and 20 nm, respectively. Furthermore, it is discovered that the computer-simulated near-field energy distribution profile, obtained by scanning over polystyrene spheres under illumination mode, falls within 5% range as compared with experimental values. The near-field absorption coefficient can be determined by this way. This will be a useful theoretical model to analyze the near-field transmission effect from others.